FIG. 1 depicts a diagram of the salient components of wireless telecommunications system 100 in the prior art. Wireless telecommunications system 100 comprises: wireless terminal 101, cellular base stations 102-1, 102-2, and 102-3, WiFi base stations 103-1 and 103-2, wireless infrastructure 111, location-based application server 112, and GPS constellation 121, interrelated as shown. Wireless telecommunications system 100 provides wireless telecommunications service to all of geographic region 120, in well-known fashion.
Wireless terminal 101 is capable of being moved and, as a result, is not necessary associated with a fixed location. There are many techniques in the prior art for estimating the current location of wireless terminal 101. The theme that is common to many of these techniques is that location of the wireless terminal is estimated based on the electromagnetic (e.g., radio, etc.) signals—in one form or another—that are processed (i.e., transmitted or received) by the wireless terminal.
In accordance with one family of techniques, the location of a wireless terminal is estimated based on the transmission range of the base stations with which it is communicating. Because the range of a base station is known to be N meters, this family of techniques provides an estimate for the location that is generally accurate to within N meters. A common name for this family of techniques is “cell identification” or “cell ID.” The principal disadvantage of the family of cell ID techniques is that there are many applications for which the accuracy of the estimate for the location it generates is insufficient.
In accordance with a second family of techniques, the location of a wireless terminal is estimated by analyzing the angle of arrival or time of arrival of the signals transmitted by the wireless terminal. A common, if somewhat inaccurate, name for this family of techniques is called “triangulation.” The principal disadvantage of the triangulation techniques is that there are many applications for which the accuracy of the estimate for the location it generates is insufficient.
In accordance with a third family of techniques, the location of a wireless terminal is estimated by a receiver in the wireless terminal that receives signals from satellites in orbit. A common name for this family of techniques is “GPS.” The principal advantage of the GPS techniques is that when it works, the estimate for the location can be accurate to within meters. The GPS techniques are disadvantageous in that they do not work consistently well indoors, in heavily-wooded forests, or in urban canyons.
In accordance with a fourth family of techniques, the location of a wireless terminal is estimated by pattern matching one or more location-dependent traits of one or more electromagnetic signals that are processed (i.e., transmitted and/or received) by the wireless terminal. Common names for this family of techniques include “RF Pattern Matching (RFPM)” and “RF Fingerprinting.”
The basic idea with pattern matching is that some traits of an electromagnetic signal remain (more or less) constant as a signal travels from a transmitter to a receiver (e.g., frequency, etc.) and some traits change (e.g., signal strength, relative multi-path component magnitude, propagation delay, etc.). A trait that changes is considered a “location-dependent” trait. Each location can be described or associated with a profile of one or more location-dependent traits of one or more electromagnetic signals. A wireless terminal at an unknown location can observe the traits and then attempt to ascertain its location by comparing the observed traits with a database that correlates locations with expected or predicted traits.
There are various modifications that can be made to the basic pattern matching technique to improve the accuracy of the estimate for the location. The principal advantage of at least some such pattern matching techniques is that they are highly accurate and work well indoors, in heavily wooded forests, and in dense urban areas (i.e., in “urban canyons”).
In regard to the various families of techniques described above, some location estimation techniques work well even in environments where the measured strengths of the different signals vary significantly, such as where signal obstructions are present, including natural obstructions such as mountains and artificial obstructions such as buildings. Meanwhile, other techniques might work best under a different set of operating conditions.
Therefore, the need exists for assessing the operating conditions of a wireless terminal, in order to determine how best to estimate its location, and then estimating its location accordingly.